Xenu's Link Sleuth - Xenus Link Sleuth checks Web sites for broken links.
LinkChecker - LinkChecker is a free, GPL licensed website validator.
DRKSpiderJava - DRKSpider is an open source website crawler (sitemap generator) and link checker. Features:
Integrity - Feature comparison of link checkers for Mac: Integrity, Integrity Plus and Scrutiny
Dead Link Checker - Check for broken links on any website
A1 Website Analyzer - Analyze websites and save data into XML, CSV etc. Extract data about internal linking and importance calculations, file sizes, download times, HTML validation errors etc. across entire websites.